The String road that joins Blackwaterfoot to Brodick has a long climb from the Brodick end and then a nice long meandering descent which has a few tight turns over wee bridges. Saw a bloke on a yellow 'bent getting up some turn of speed on the way down last week. Sometimes lots of gravel at these twisty bits so beware. The Post Office at Blackwaterfoot will make up rolls and drinks to order. Bakery ( down the lane at side of the Kinloch) in summer is open 0930-1300, but not on Wed or Sun, and has lots of cake and sticky goodies to top up energy levels. Harbour shop ( 0900-1700)has a sandwich, drink deal on at the moment too. Kinloch welcomes cyclists but food a bit dearer but well worth it, IMHO.
If you do it Brodick to B'foot, stop at the top of the hill where you see a couple of solar panel thingies on poles( there's a path to a seat at the top on the RHS) and admire the view.
The Ross road goes from Lamlash to Kilmory (funnily it is 8 miles from Lamlash to Kilmory but 9 miles from Kilmory to Lamlash, according to the signs). It is single track with passing places and has a steep start then is very twisty in bits.There have been one or two grumbling comments in the Arran Banner about cyclists bombing down the road 3 abreast. Bumbling drivers are sometimes encountered on this road but not often, but keep your wits about you as some don't know what a passing place is used for (tourists?).
The Coffee Pot at Whiting Bay is also a good place for eats but best to take away as finding a seat can be impossible at times.
Anyone interested in extreme mountain biking might like the path from Lochranza to Laggan cottage (then back via the cock of Arran, the most northerly point). We walked it last week. The Lochranza to Laggan path is only about 3 or 4 miles but its very steep and we couldn't believe it when we saw mountain bike tyre tracks in the mud.
As you might have gathered, I have a long acquaintance with Arran so if I can be of any help, please just ask.